Systems including distance-measuring sensors are particularly used in systems for parking support for a driver of a motor vehicle. Using the distance measuring sensors, the distance between the vehicle and an object is recorded. For this purpose, a signal is sent by the sensor in customary sensors and an echo reflected by an object is received. From the propagation time of the signal between the sending of the signal and the reception of the echo one is able to ascertain the distance of the object from the sensor. Sensors used for the distance measurement are currently ultrasonic sensors, radar sensors, infrared sensors or LIDAR sensors, for example.
It is common to all these sensors that the signal, sent by an object that is located in the emission cone, is reflected and the echo is received by the sensor. Information on the direction towards the object cannot be ascertained thereby.
If the emission cone of the sent signal intersects with the ground, such as a road on which the vehicle is traveling, the ground is also detected as an object in the surroundings of the vehicle. Since, however, the ground does not represent any obstacle, the detection of the ground and the hint of an object at a distance of the spacing from the ground to the driver is not desired.
A method is described in German Published Application DE-T 601 17 407, by which, when using radar sensors, one is able to exclude the ground as an object that is able to be an obstacle. For this, after the installation of the sensor, a measurement is carried out, and the measured signals are stored as background noise. This background noise is then subtracted from the measured signals, so as to detect objects.
The method described in DE-T 601 17 407 cannot be used on ultrasonic sensors, however. At this time, the setting of ultrasonic sensors takes place after their installation in the vehicle. For the purpose of detecting only obstacles, and not the ground, this yields a restriction in the height of installation of ultrasonic sensors and a restriction in the visual direction of the sensors. In addition, the use in commercial vehicles, in particular, is possible only to a limited degree, since, on account of big differences in height because of varying loading states and/or the load leveling system of vehicles, the setting of the sensor would have to be adjusted in each case to the level of the vehicle, so as to prevent, at varying distances of the sensors from the ground, the roadway from being detected.